This invention relates to apparatus and methods for detecting misplaced items characterized by residual magnetic fields. More particularly, the present invention relates to a detection system including a portable gradiometer of improved design for indicating the proximity of an item such as a residually magnetized misplaced tool.
In some work and maintenance environments, such as ground maintenance of aircraft, the misplacement and loss of small items such as hand tools and the like may present grave hazards and sometimes result in damage or destruction of property and injury or loss of human life.
Magnetic tagging of items such as tools, has been proposed in the prior art in order to facilitate locating such items in the event they have been lost or misplaced. One prior approach was set forth in U.S. Pat. No. 3,587,583 to Greenberg, issued June 28, 1971. Therein, magnetized particles were secured to surgical sponges. Prior to the completion of an operation, the patient was scanned by a magnetodiode sensor apparatus to detect residual magnetic fields which would have indicated a lost or misplaced sponge.
Other prior art approaches were disclosed in U.S. Pat. No. 3,292,080 to Trikilis, issued Dec. 13, 1966 and entitled System and Method for Preventing Pilferage by Detection of Magnetic Fields., RCA Technical Notes, TN No. 675, June 1966 entitled "Intra-Uterine Device with Means for External Detection (permanent magnets)"; and Swiss Pat. No. 355,357 to Stollner, issued August 1961.
While those approaches acknowledged the utility of residual magnetic tagging of small items placed in or about the person, there was no teaching that this approach could be utilized in much larger work environments, particularly the ground maintenance environment associated with large aircraft.
One significant drawback of prior approaches was the unavailability heretofore of portable detection apparatus having sufficient sensitivity and directivity to detect and indicate low level residual magnetic fields at distances greater than a few inches away.
Another drawback of prior approaches was the absence of a portable detector having a hand held probe with known directional characteristics to facilitate pinpointing lost items in nonvisible locations, such as inside engine cowlings.
A further drawback of prior approaches was the need to provide the residual magnetism as part of the manufacturing process for items, such as surgical sponges, capable of being misplaced or lost.